Lung cancer is the most common worldwide cause of cancer mortality. In the United States, lung cancer is the second most prevalent cancer in both men and women and will account for more than 174,000 new cases per year and more than 162,000 cancer deaths. In fact, lung cancer accounts for more deaths each year than from breast, prostate and colorectal cancers combined2.
The high mortality (80-85% in five years), which has shown little or no improvement in the past 30 years, emphasizes the fact that new and effective tools to facilitate early diagnoses prior to metastasis to regional nodes or beyond the lung are needed6.
High risk populations include smokers, former smokers, and individuals with markers associated with genetic predispositions91-93. Because surgical removal of early stage tumors remains the most effective treatment for lung cancer, there has been great interest in screening high-risk patients with low dose spiral CT (LDCT)12,14,15,94. This strategy identifies non-calcified pulmonary nodules in approximately 30-70% of high risk individuals but only a small proportion of detected nodules are ultimately diagnosed as lung cancers (0.4 to 2.7%)16,95,96. Currently, the only way to differentiate subjects with lung nodules of benign etiology from subjects with malignant nodules is an invasive biopsy, surgery, or prolonged observation with repeated scanning. Even using the best clinical algorithms 20-55% of patients selected to undergo surgical lung biopsy for indeterminate lung nodules, are found to have benign disease15 and those that do not undergo immediate biopsy or resection require sequential imaging studies. The use of serial CT in this group of patients runs the risk of delaying potential curable therapy, along with the costs of repeat scans, the not-insignificant radiation doses, and the anxiety of the patient.
Ideally, a diagnostic test would be easily accessible, inexpensive, demonstrate high sensitivity and specificity, and result in improved patient outcomes (medically and financially). Efforts are in progress to develop non-invasive diagnostics using sputum, blood or serum and analyzing for products of tumor cells, methylated tumor DNA7,8, single nucleotide polymorphism (SNPs)9 expressed messenger RNA10 or proteins11. This broad array of molecular tests with potential utility for early diagnosis of lung cancer has been discussed in the literature. Although each of these approaches has its own merits, none has yet passed the exploratory stage in the effort to detect patients with early stage lung cancer, even in high-risk groups, or patients which have a preliminary diagnosis based on radiological and other clinical factors12. A simple blood test, a routine event associated with regular clinical office visits, would be an ideal diagnostic test.
One established method to achieve the goal of genetic diagnosis has been the use of microarray signatures from tumor tissue20. This approach has been tested and validated by numerous investigators89. An increasing number of studies have shown that peripheral blood mononuclear cells (PBMC) profiles can be used to diagnose and classify systemic diseases, including cancer, and to monitor therapeutic response.21 The validity of using PBMC profiles in patients with cancer has been previously reported in the use of microarrays to compare PBMC from patients with late stage renal cell carcinoma compared to normal controls20,42. A more recent publication43 describes the development of a 37 gene classifier for detecting early breast cancer from peripheral blood samples with 82% accuracy. Another study identified gene expression profiles in the PBMC of colorectal cancer patients that could be correlated with response to therapy44. Some of the present inventors previously suggested22 that chemokines and cytokines released by malignant cells could impose a tumor specific signature on immune cells of patients with non-hematopoietic cancers. Gene expression profiles have now been generated from PBMC that identify blood signatures associated with a variety of cancers, including metastatic melanoma23, breast24, renal25,26 and bladder cancer27. Most of these studies focused on late stage cancers or response to therapy and used younger healthy control groups for comparison.
While the effect of chronic obstruction pulmonary disease (COPD) on PBMC gene expression is relatively unstudied to date, there are some limited reports about the effect of cigarette smoke33. Exposure of peripheral blood lymphocytes (PBL) ex vivo to cigarette smoke induced many changes in gene expression34. Changes could be detected in the transcriptosome of blood neutrophils in COPD patients versus normals35. One study distinguished “between 85 individuals exposed and unexposed to tobacco smoke on the basis of mRNA expression in peripheral leukocytes”36. No data is apparently available regarding similar changes in blood that may be present in former-smokers. Gene expression in airway epithelia of smokers, ex-smokers and non-smokers has been compared37. Although many clinical manifestations of smoking rapidly returned to normal after smoking cessation, there was a subset of genes whose expression remained altered. Differential gene hypermethylation38 and dysregulated macrophage cytokine production33 have also been linked to cigarette smoke. However, to date, there are no reports of gene expression profile or signature useful in the diagnosis of lung cancer.
Despite recent advances, the challenge of cancer treatment remains to target specific treatment regimens to pathogenically distinct tumor types, and ultimately personalize tumor treatment in order to maximize outcome. Hence, a need exists for tests that simultaneously provide predictive information about patient responses to the variety of treatment options. In particular, once a patient is diagnosed with cancer, there is a strong need for methods that allow the physician to predict the expected course of disease, including the likelihood of cancer recurrence, long-term survival of the patient, and the like, and select the most appropriate treatment option accordingly. There also remains a need in the art for a less invasive diagnostic test that could more accurately determine the risk of malignant disease in patients with lung nodules and would reduce unnecessary surgery, biopsies, PET scans, and/or repeated CT scans.